Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils

Coprecipitation with Ferrihydrite Inhibits Mineralization of Glucuronic Acid in an Anoxic Soil

“…Moreover, the fact that the amount of solid-associated Fe(II) continually increased in the 13 GluC treatment without maintenance of 13 C mineralization rates suggests that, if sorbed to the soil matrix, the 13 C-glucuronic acid may have preferentially sorbed to aluminosilicates rather than SRO iron minerals, both of which were abundant in this soil. 34 Iron Protection of OC Is Enhanced at Lower Temperatures. In the 12 °C incubations, total amounts of CO 2 derived from both the native SOM and the 13 C-glucuronic acid were lower than in the 25 °C incubations (Figure S8c), as is expected due to decreases in microbial activity at lower temperatures.…”

“…34 Recently, we showed that ferrihydrite in Icelandic wetland soils is rapidly reduced and re-precipitated during redox cycles. 34 Thus, it is likely that the native ferrihydrite of the soil horizon included here formed in situ and therefore precipitated in the presence of abundant OM (Table S1). As such, it is likely that the native ferrihydrite showed higher structural disorder than the synthetic 57 Fe-ferrihydrite.…”

“…For this study, soil from a Gleyic Andosol (GA; Icelandic soil classification system), a typical soil type found across north and western Iceland, was included. Specifically, a subsoil horizon (60–72 cm depth) from the Hestur_GA soil profile, , located in the Borgarfjördur catchment in western Iceland (Figure S1), was chosen. The characterization of horizons from this soil profile was included in a previous publication .…”

“…Specifically, a subsoil horizon (60–72 cm depth) from the Hestur_GA soil profile, , located in the Borgarfjördur catchment in western Iceland (Figure S1), was chosen. The characterization of horizons from this soil profile was included in a previous publication . For this study, fresh soil samples were collected in July 2020.…”

“…Iron-bound carbon represents a high amount of total carbon in soils and sediments, ,, storing up to 40% of total soil carbon under oxic conditions. , In agreement, the effectiveness of iron mineral protection of adsorbed OC under oxic soil conditions has been consistently demonstrated in aerobic soil incubations, ,, where mineralization of MAOM has been shown to be reduced by >99.5% and substrate sorption in soils with high clay content (<0.002 mm size fraction) has been shown to limit substrate mineralization. , However, in the absence of O 2 , Fe­(III) acts as a terminal electron acceptor for microorganisms during anaerobic respiration of organic matter. , Electron transfer reactions induce the reductive dissolution, recrystallization, or transformation of iron minerals, , with direct implications for the solubilization and mineralization of MAOM. The reductive dissolution of Fe­(III) in mineral aggregates or in Fe­(III)–OC coprecipitates releases adsorbed or occluded OC to soil solution. − Mobilized OC, found as DOC , or in organic-Fe/Al colloids, , may further form stable complexes with dissolved Fe, be transported to deeper soil horizons, or may be subsequently mineralized . Moreover, microbial use of Fe­(III) as an electron acceptor can directly result in CO 2 production through the metabolic coupling of OC oxidation to Fe­(III) reduction. , Thus, under reducing soil conditions, mineralization of SOM can even be stimulated by the addition of Fe­(III) minerals acting as electron acceptors. , In anoxic soils, microbial Fe reduction may account for up to 44% of anaerobic OC mineralization …”